Since Al has superior corrosion resistance and mouldability, as well as lightness, it is widely used in many industrial fields, particularly the automobile industry, as the most universally used metal material, after steel materials. Recently, in order to make automobiles lighter, the use of Al plate has gradually been increasing. However, Al plate is more difficult to mould than steel plate, and easily cracks during moulding; hence there are major problems, such as shape lmitations during design.
Because of this, when pressing Al plate, automobile manufacturers often use liquid lubricating oils or solid lubricants with superior lubricating properties rather than using the normal mineral oil lubricants. The solid lubricants are used to increase press mouldabuity by forming a lubricant film on the Al plate material beforehand. Thus, in the subsequent assembly steps, bonding processes and welding processes are performed on the pressed products without removing the lubricant, and the lubricant is removed in a degreasing step after completion of the assembly steps.
However, with the aforesaid method, because the bonding processes and welding processes are performed with the lubricant still coated on the product after pressing, the residual lubricant causes poor bonding and poor welding, and as a result productivity may decrease and product quality may deteriorate.